A method of forecasting, allocating and scheduling in a single or multi-site skills-based contact or call center environment organized into a hierarchy of zero or more business units at a first, upper level, one or more contact types at a second, intermediate level, and one or more management units at a third, lower level. In a gas exchanging step, the impurity gas in the sealed chamber is first exhausted through an electromagnetic valve provided with a check valve and a gas exhaust pipe, using a gas exhaust pump and then, a high-purity nitrogen gas is supplied from a gas bomb through a gas supply pipe and an electromagnetic valve provided with a check valve to the sealed chamber. In some embodiments a new selection value is determined from a current selection value and a derivative parameter stored as a portion of a set of stream parameters.